Screen coating composition and method for applying same

ABSTRACT

A substantially water-free, water-washable, energy-curable composition includes an epoxy oligomer and/or urethane oligomer having at least two ethylenically unsaturated moieties, at least one alkoxylated polyol monomer having at least two ethylenically unsaturated moieties and capable of being copolymerized with the oligomer, and a surface active agent capable of being integrated into the molecular structure of the cured polymer and further capable of rendering the uncured composition dispersible in water. Optionally, the composition can contain a photoinitiator. The composition is self-dispersible in water and is especially suitable for use as a coating material for a printing screen.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a water-free, water-washable,energy-curable, polymer-forming composition, especially useful as aprint screen coating, and a method for applying same.

2. Background of the Art

In silk screen printing, the ink is forced onto a printing substratethrough a stencil, or "mask", having a porous screen area configured inthe shape of the indicia to be printed, such as letters or graphicimages. The printing substrate can be paper, textile, metal, ceramic,polymer film, and the like. The screen can be a gauze or mesh fabricatedfrom metal, textile fabric such as silk or cotton, or various polymermaterials.

The mask is generally prepared by coating a screen with a curablecomposition, curing the composition, and then engraving the indicia. Theengraved areas are porous, thereby permitting ink to be forced throughthe screen onto the printing substrate to print the indicia.

After printing, the ink on the substrate is cured or hardened by any ofseveral methods such as, for example, exposure of the ink to energy suchas heat or radiation (e.g. ultraviolet, electron beam, and the like),evaporation of a solvent in the ink composition, or oxidation hardeningof drying oil components (e.g linseed oil, tung oil), and the like.

The three main technologies being practiced today which make up the bulkof the coatings and inks include solvent borne, water borne, and zerovolatile organic compounds (VOC). Solvent borne and water borne systemsproduce coatings which are washable. Water washability is a desiredfeature of a coating composition since the coating application equipmentneeds to be cleaned for reuse. However, there has been a technologicalpush to eliminate organic solvents and water in such compositions.Organic solvents present environmental health concerns. And both solventbased and water based systems are energy intensive, requiring dryingovens to remove the solvent or water. For example, thermally induceddrying and curing of coated screen fabric typically requires about 7,000to 12,000 kilojoules of energy per kilogram of fabric as well as a longcuring time, typically several hours Consequently, what is desired is awaterless, yet water-dispersible, zero VOC composition which would beparticularly useful as a coating for a print screen.

SUMMARY OF THE INVENTION

In accordance with the present invention, a substantially water-free,water-washable, energy-curable, polymer-forming composition is providedwhich comprises:

a) an oligomer selected from the group consisting of epoxy oligomer andurethane oligomer, said oligomer having at least two polymerizableethylenically unsaturated moieties;

b) at least one alkoxylated polyol monomer having at least twopolymerizable ethylenically unsaturated moieties and capable of beingcopolymerized with oligomer component (a) to provide a solid curedpolymer when exposed to energy-polymerizing conditions; and,

c) at least one surface active agent capable of being integrated intothe molecular structure of the polymer resulting from thecopolymerization of (a) and (b) either by covalent bonding or byhydrogen bonding, and further capable of rendering said compositionwater-dispersible.

Also provided herein is a method for coating a screen with theaforementioned composition employing applicator means which can bewashed with water.

The foregoing composition contains substantially no VOCs and is readilydispersible in water. Another advantage of this composition is that itsignificantly reduces the amount of energy and time required to effectcuring.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the present invention is particularly applicable to coatings forprint screens, it should be understood that any coating application orsubstrate, for printing or non-printing purposes, is within its scope.Percentages of materials are by weight unless stated otherwise. Notethat all quantities appearing hereinafter shall be understood to bemodified by the term "about" except in the Examples and unless indicatedotherwise.

The substantially water-free, water-washable, energy-curable,poly-forming composition herein includes an epoxy oligomer and/orurethane oligomer having at least two polymerizable ethylenicallyunsaturated moieties, an alkoxylated polyol monomer having at least twoethylenically unsaturated moieties and a surface active agent which iscopolymerizable with the oligomer and/or monomer.

An aliphatic and/or aromatic urethane oligomer may optionally beemployed instead of, or in addition to, the epoxy oligomer. The urethaneoligomer component is preferably a urethane acrylate such as, forexample, PHOTOMER® 6008 available from Henkel Corporation. However, theepoxy oligomer is preferred.

Also, the epoxy oligomer may optionally be accompanied by polyesteracrylate oligomer, trimethylol propane dimerester tetraacrylateoligomer, or dipolyoxypropylene glycerol adipate oligomer.

Generally, the energy-curable composition of the present inventionincludes the following component weight percentages:

    ______________________________________                                        Oligomers          30%-70%                                                      Monomers 30%-70%                                                              Surfactants 0.1% to about 20%                                                 Photoinitiators 0-10%                                                       ______________________________________                                    

The epoxy oligomer can be prepared by reacting an epoxide with anunsaturated acid such as acrylic or methacrylic acid, optionally in thepresence of a polyamide derived from a polymerized fatty acid.

In one embodiment the epoxy acrylate oligomer is derived from a compoundhaving the formula:

    R.sup.1 --[--CH.sub.2 --CHOH--CH.sub.2 --O(O)C--CH═CH.sub.2 ].sub.n

wherein R¹ is an aliphatic, aromatic or arene moiety having at least twocarbon atoms and at least two oxido residues, and n is an integer offrom 2 to 6.

Useful epoxides include the glycidyl ethers of both polyhydric phenolsand polyhydric alcohols, epoxidized fatty acids or drying oil acids,epoxidized diolefins, epoxidized di-unsaturated acid esters, as well asepoxidized unsaturated polyesters, preferably containing an average ofmore than one epoxide group per molecule. The preferred epoxy compoundswill have a molecular weight of from 300 to 600 and an epoxy equivalentweight of between 150 and 1,200.

Representative examples of the epoxides include condensation products ofpolyphenols and (methyl)epichlorohydrin. For the polyphenols, there maybe listed bisphenol A, 2,2'-bis(4-hydroxyphenyl)methane (bisphenol F),halogenated bisphenol A, resorcinol, hydroquinone, catechol,tetrahydroxyphenylethane, phenol novolac, cresol novolac, bisphenol Anovolac and bisphenol F novolac. There may also be listed epoxycompounds of the alcohol ether type obtainable from polyols such asalkylene glycols and polyalkylene glycols, e.g. ethylene glycol,1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol,1,6-hexanediol, neopentyl glycol, glycerine, diglycerol,trimethylolpropane, pentaerythritol, inositol, sorbitol, polyethyleneglycol, polypropylene glycol, polytetrahydrofuran, (i.e.,poly(1,4-butanediol), which is obtainable under the designationTERATHONE® from DuPont), and alkylene oxide-adduct of bisphenols, and(methyl)epichlorohydrin; glycidyl amines obtainable from anilines suchas diaminodiphenylmethane, diaminophenylsulfone and p-aminophenol, and(methyl)epichlorohydrin; glycidyl esters based on acid anhydrides suchas phthalic anhydride and tetrahydro- or hexahydro-phthalic anhydride;and alicyclic epoxides such as 3,4-epoxy-6-methylcyclohexylmethyl and3,4-epoxy-6-methylcyclohexyl carboxylate.

Glycidyl polyethers of polyhydric phenols are made from the reaction ofa polyhydric phenol with epihalohydrin or glycerol dihalohydrin, and asufficient amount of caustic alkali to combine with the halogen of thehalohydrin. Glycidyl ethers of polyhydric alcohols are made by reactingat least about 2 moles of an epihalohydrin with 1 mole of a polyhydricalcohol such as ethylene glycol, pentaerythritol, etc., followed bydehydrohalogenation.

In addition to polyepoxides made from alcohols or phenols and anepihalohydrin, polyepoxides made by the known peracid methods are alsosuitable. Epoxides of unsaturated esters, polyesters, diolefins and thelike can be prepared by reacting the unsaturated compound with aperacid. Preparation of polyepoxides by the peracid method is describedin various periodicals and patents and such compounds as butadiene,ethyl linoleate, as well as di- or tri-unsaturated drying oils or dryingoil acids, esters and polyesters can all be converted to polyepoxides.Epoxidized drying oils are also well known, these polyepoxides usuallybeing prepared by reaction of a peracid such as peracetic acid orperformic acid with the unsaturated drying oil according to U.S. Pat.No. 2,569,502.

In certain embodiments, the diepoxide is an epoxidized triglyceridescontaining unsaturated fatty acids. The epoxidized triglyceride may beproduced by epoxidation of one or more triglycerides of vegetable oranimal origin. The only requirement is that a substantial percentage ofdiepoxide compounds should be present. The starting materials may alsocontain saturated components. However, epoxides of fatty acid glycerolesters having an iodine value of 50 to 150 and preferably 85 to 115 arenormally used. For example, epoxidized triglycerides containing 2% to10% by weight of epoxide oxygen are suitable. This epoxide oxygencontent can be established by using triglycerides with a relatively lowiodine value as the starting material and thoroughly epoxidizing them orby using triglycerides with a high iodine value as starting material andonly partly reacting them to epoxides. Products such as these can beproduced from the following fats and oils (listed according to theranking of their starting iodine value): beef tallow, palm oil, lard,castor oil, peanut oil, rapeseed oil and, preferably, cottonseed oil,soybean oil, train oil, sunflower oil, linseed oil. Examples of typicalepoxidized oils are epoxidized soybean oil with an epoxide value of 5.8to 6.5, epoxidized sunflower oil with an epoxide value of 5.6 to 6.6,epoxidized linseed oil with an epoxide value of 8.2 to 8.6 andepoxidized train oil with an epoxide value of 6.3 to 6.7.

Further examples of polyepoxides include the diglycidyl ether ofdiethylene glycol or dipropylene glycol, the diglycidyl ether ofpolypropylene glycols having molecular weight up to, for example, 2,000,the triglycidyl ether of glycerine, the diglycidyl ether of resorcinol,the diglycidyl ether of 4,4'-isopropylidene diphenol, epoxy novolacs,such as the condensation product of 4,4'-methylenediphenol andepichlorohydrin and the condensation of 4,4'-isopropylidenediphenol andepichlorohydrin, glycidyl ethers of cashew nut oil, epoxidized soybeanoil, epoxidized unsaturated polyesters, vinyl cyclohexene dioxide,dicyclopentadiene dioxide, dipentene dioxide, epoxidized polybutadieneand epoxidized aldehyde condensates such as 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate.

Particularly preferred epoxides are the glycidyl ethers of bisphenols, aclass of compounds which are constituted by a pair of phenolic groupsinterlinked through an intervening aliphatic bridge. While any of thebisphenols may be used, the compound 2,2-bis (p-hydroxyphenyl) propane,commonly known as bisphenol A, is more widely available in commerce andis preferred. While polyglycidyl ethers can be used, diglycidyl ethersare preferred. Especially preferred are the liquid BisphenolA-epichlorohydrin condensates with a molecular weight in the range offrom 300 to 600.

The acid component is comprised of an ethylenically unsaturated acid.Particularly suitable ethylenically unsaturated monocarboxylic acid arethe alpha, beta-unsaturated monobasic acids. Examples of suchmonocarboxylic acid monomers include acrylic acid,beta-acryloxypropionic acid, methacrylic acid, crotonic acid, andalpha-chloroacrylic acid. Preferred examples are acrylic acid andmethacrylic acid. Also suitable acid components are adducts ofhydroxyalkyl acrylates or hydroxyalkyl methacrylates and the anhydridesof dicarboxylic acids such as, for example, phthalic anhydride, succinicanhydride, maleic anhydride, glutaric anhydride, octenylsuccinicanhydride, dodecenylsuccinic anhydride, chlorendic anhydride,tetrahydrophthalic anhydride, hexahydrophthalic anhydride andmethyltetrahydrophthalic anhydride. Such adducts can be prepared bymethods of preparative organic chemistry known in the art. The acidcomponent can also contain other carboxylic acids. In certainembodiments, the acid component will be comprised of a minor amount,e.g. less than 50% of the total acid equivalents, more typically lessthan 20% of the total acid equivalents, of a fatty acid. The fatty acidsare saturated and/or unsaturated aliphatic monocarboxylic acidscontaining 8 to 24 carbon atoms or saturated or unsaturatedhydroxycarboxylic acids containing 8 to 24 carbon atoms. The carboxylicacids and/or hydroxycarboxylic acids may be of natural and/or syntheticorigin. Examples of suitable monocarboxylic acids are caprylic acid,2-ethylhexanoic acid, capric acid, lauric acid, myristic acid, palmiticacid, palargonic acid, palmitoleic acid, stearic acid, isostearic acid,oleic acid, elaidic acid, petroselic acid, linoleic acid, linolenicacid, elaeostearic acid, conjuene fatty acid, ricinoleic acid, arachicacid, gadoleic acid, behenic acid, erucic acid and brassidic acid andthe technical mixtures thereof obtained, for example, in the pressurehydrolysis of natural fats and oils, in the oxidation of aldehydes fromRoelen's oxo synthesis, or as monomer fraction in the dimerization ofunsaturated fatty acids. In a particularly preferred embodiment, thefatty acid is derived from technical mixtures of the fatty acidsmentioned which are obtainable in the form of the technical mixturestypically encountered in oleochemistry after the pressure hydrolysis ofoils and fats of animal or vegetable origin, such as coconut oil, palmkernel oil, sunflower oil, rape oil, rapeseed oil and coriander oil andbeef tallow. However, the fatty acid may also contain a branched fattyacid residue, for example the residue of 2-ethyl hexanoic acid,isopalmitic acid or isostearic acid.

Preferred fatty acids are mixtures obtained from natural sources, e.g.palm oil, palm kernel oil, coconut oil, rapeseed oil (from oldhigh-erucic acid plants or from new low-erucic acid plants, a.k.a.canola oil), sunflower oil (from old low-oleic plants or from newhigh-oleic plants), castor oil, soybean oil, cottonseed oil, peanut oil,olive oil, olive kernel oil, coriander oil, castor oil, meadowfoam oil,chaulmoogra oil, tea seed oil, linseed oil, beef tallow, lard, fish oiland the like. Naturally occurring fatty acids typically are present astriglycerides of mixtures of fatty acids wherein all fatty acids have aneven number of carbon atoms and a major portion by weight of the acidshave from 12 to 18 carbon atoms and are saturated or mono-, di-, ortri-unsaturated.

The preferred epoxy resins, i.e., those made from bisphenol A, will havetwo epoxy groups per molecule. Thus, the product of a reaction withacrylic or methacrylic acid will contain an epoxy (meth)acrylatecompound having a main chain of polyepoxide and both terminals of a(meth)acrylate group, respectively. Accordingly, the stoichiometricamount of acrylic acid to form a diacrylate adduct would be two moles ofacid for each two epoxy groups. In practice, however, it is preferred touse an amount of acid slightly in excess of the amount necessary tocover both epoxy groups. Therefore, the amount of acrylic acid reactedis typically between 2.001 moles to 2.1 moles, and more typicallybetween 2.01 and 2.05 moles of acid per two epoxy groups.

Alternatively, the reaction of the epoxide and the acid can take placein the presence of a polyamide derived from a polymerized fatty acid.The polyamide preferably has a number average molecular weight of lessthan 10,000 grams/mole. Low melting polyamide resins melting within theapproximate range of 90° C. to 130° C. may be prepared from polymericfatty acids and aliphatic polyamines. Typical of the polyamines whichmay be used are ethylene diamine, diethylene triamine, triethylenetetramine, tetraethylene pentamine, 1,4-diaminobutane,1,3-diaminobutane, hexamethylene diamine, piperazine, isophoronediamine, 3-(N-isopropylamine)-propylamine, 3,3'-iminobispropylamine, andthe like. A preferred group of these low melting polyamides are derivedfrom polymeric fatty acids, and ethylene diamine and are solid at roomtemperature.

Suitable such polyamides are commercially available under the tradedesignation of VERSAMID polyamide resins, e.g. VERSAMID 335, 750 and744, and are amber-colored resins having a number average molecularweight up to 10,000, preferably from 1,000 to 4,000 and a softeningpoint from below room temperature to 190° C.

The preferred polyamide is VERSAMID 335 polyamide which is commerciallyavailable from Henkel Corporation and has an amine value of 3, a numberaverage molecular weight of 1699, as determined by gel permeationchromatography (GPC) using a polystyrene standard, and a polydispersityof 1.90.

The preparation of such VERSAMID polyamide resins is well known and byvarying the acid and/or functionality of the polyamine, a great varietyof viscosities, molecular weights and levels of active amino groupsspaced along the resin molecule can be obtained. Typically, the VERSAMIDpolyamide resins useful herein have amine values from 0 to 25,preferably 0 to 10, more preferably 0 to 5; viscosities of from about 1to 30 poises (at 160° C.) and polydispersities of less than 5. The aminevalue and number average molecular weight of the polyamide can bedetermined as described in U.S. Pat. No. 4,652,492 (Seiner et. al.), thedisclosure of which is incorporated herein by reference.

The polyamide is incorporated into the composition in an amount notexceeding 50% by weight based on the combined weight of the epoxide andacid components and the polyamide. Preferably, an amount not exceeding25% by weight is utilized and most preferred is an amount of from 5% to15% by weight.

The reaction between the epoxide and acid can be performed over a widerange of temperatures, e.g. from 40° C. to 150° C., more typically from50° C. to 130° C. and preferably between 90° C. and 110° C., atatmospheric, sub-atmospheric or superatmospheric pressure; preferably inan inert atmosphere. Esterification is continued until an acid number of2 to 15 is obtained. This reaction ordinarily takes place in 8 to 15hours. To prevent premature or undesirable polymerization of the productor the reactants, it is advantageous to add a vinyl inhibitor to thereaction mixture. Suitable vinyl polymerization inhibitors includetert-butylcatechol, hydroquinone, 2,5-ditertiarybutylhydroquinone,hydroquinonemonoethyl ether, etc. Advantageously, the inhibitor isincluded in the reaction mixture at a concentration of 0.005 to 0.1% byweight based on the total of the reagents.

The reaction between the epoxide and the acid proceeds slowly whenuncatalyzed, and can be accelerated by suitable catalysts whichpreferably are used, such as, for example, the tertiary bases such astriethyl amine, tributylamine, pyridine, dimethylaniline, tris(dimethylaminomethyl)-phenol, triphenyl phosphine, tributyl phosphine,tributylstilbine; alcoholates such as sodium methylate, sodium butylate,sodium methoxyglycolate, etc.; quaternary compounds such astetramethylammonium bromide, tetramethylammonium chloride,benzyl-trimethylammonium chloride, and the like. At least 0.01 percent,based on total weight of reagents, preferably at least 0.1 percent, ofsuch catalyst is desirable.

Typical examples of suitable monomers which can be used and added to thereaction mixture before or during the reaction, or added after thereaction, as a reactive diluent, are the vinyl or vinylidene monomerscontaining ethylenic unsaturation, and which can copolymerized with thecompositions of this invention are, styrene, vinyl toluene, tertiarybutyl styrene, alpha-methyl-styrene, monochlorostyrene, dichlorostyrene,divinylbenzene, ethyl vinyl benzene, diisopropenyl benzene, methylacrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate,acrylonitrile, methacrylonitrile, the vinyl esters, such as vinylacetate and the monovinyl esters of saturated and unsaturated aliphatic,monobasic and polybasic acids, such as the vinyl esters of the followingacids: propionic, isobutyric, caproic, oleic, stearic, acrylic,methacrylic, crotonic, succinic, maleic, fumaric, itaconichexahydrobenzoic, citric, tartaric, etc., as well as the correspondingallyl, methallyl, etc., esters of the aforementioned acids, the itaconicacid monoesters and diesters, such as the methyl, ethyl, butyl esters,etc.; the maleic and fumaric acid monoesters, diesters and their amideand nitrile compounds, such as diethyl maleate, maleyl tetramethyldiamide, fumaryl dinitrile, dimethyl fumarate; cyanuric acid derivativeshaving at least one copolymerizable unsaturated group attached directlyor indirectly to the triazine ring such as diallyl ethyl cyanurate,triallyl cyanurate, etc., ethers such as vinyl allyl ether, divinylether, diallyl ether, resorcinol divinyl ether, etc., diallylchlorendate, diallyl tetrachloro phthalate, diallyl tetrabromophthalate,dibromopropargyl acrylate, as well as the partial fusible or solublepolymerizable polymers of the hereinabove listed monomers, etc.

In preparing the polymerizable compositions containing the reactionproduct of this invention and one or more of the monomers of the typelisted hereinabove, the relative amount of the monomers can varybroadly. In general, however, the monomer or monomers are used at lessthan 50% by weight of the composition, typically in the range of about1% to 30% by weight, and more typically in the range of 5% to 15% byweight.

Epoxy oligomers prepared by reacting an epoxide with acrylic acid in thepresence of a polyamide derived from a polymerized fatty acid possessthe advantage of being thixotropic. The viscosity of compositionscontaining such oligomers decreases with the application of increasingagitation or shear stress and gradually returns to its former viscousstate when allowed to rest. Thus, the composition exhibits lowerviscosity when in the process of being applied to a substrate under theapplication of force or pressure. However, once the coating has beenapplied it resumes its high viscosity state and tends to remain on thesubstrate without running.

Also, epoxy oligomer may optionally be accompanied by polyester acrylateoligomer, trimethylol propane dimerester tetraacrylate oligomer, ordipolyoxypropylene glycerol adipate oligomer.

Referring now to the alkoxylated polyol component of the compositiondescribed herein, the preferred alkoxylated polyol monomer has theformula.

    R.sup.2 --[--(Y).sub.x --R.sup.3 --CH═CH--R.sup.4 ].sub.m

wherein R² is an aliphatic, aromatic or arene moiety having at least twocarbon atoms and at least two oxido residues, Y is an alkylene oxidemoiety and x is an integer of from 2 to 6, R³ is a linkage group capableof joining the alkylene oxide moiety Y and the --CH═CH-- group, R⁴ ishydrogen or --C(O)OR⁵ wherein R¹ is hydrogen or an alkyl group of from 1to 22 carbon atoms, and m is an integer of from 2 to 6.

More particularly, R² can be an ethylene glycol residue, propyleneglycol residue, trimethylol propane residue, pentaerythritol residue,neopentyl glycol residue, glyceryl residue, diglyceryl residue, inositolresidue, sorbitol residue, hydroquinone residue, catechol residue, orbisphenol residue (e.g bisphenol A). R² can also be selected fromsaturated or unsaturated straight or branched chain aliphatic moietiesof from 6 to 24 carbon atoms such as epoxidized soy bean oil residue.Alternatively, R² can be polyethylene glycol, or ethyleneoxide/propylene oxide copolymer.

Y is preferably an ethylene oxide or propylene oxide residue.

R³ can optionally be, for example, the linking groups --O--, --O(O)C--,--OCH₂ CH₂ --, or --OCH₂ CHOHCH₂ O(O)C--.

The alkoxylated polyol monomer component preferably comprises a mixtureof at least one alkoxylated polyol diacrylate such as, for example,bisphenol A ethoxylate diacrylate and/or neopentyl glycol propoxylatediacrylate, and at least one alkoxylated polyol triacrylate such as, forexample trimethylolpropane ethoxylate triacrylate.

A preferred composition includes 10% to 15% by weight of neopentylglycol propoxylate diacrylate, 5% to 10% bisphenol A ethoxylatediacrylate, and 15% to 20% trimethylolpropane ethoxylate triacrylatebased on total composition weight. Preferably, also, the epoxy oligomercomponent used in conjunction with the alkoxylated polyol monomercomponent is obtained by reacting a diepoxide such as a diglycidyl etherof a dihydric phenol (e.g. bisphenol A) with an unsaturated acidcomponent (e.g. acrylic acid) in the presence of a polyamide derivedfrom a fatty acid.

Referring now to the surface active agent component, photopolymerizableprint screen coating pastes are water insoluble, hence the need for asurface active agent capable of providing water-dispersibility so thatthe uncured coating paste can be washed off the application equipment.It is most efficient to include the surface active agent as part of thescreen printing ink composition rather than as a component in the washwater. The surface active agents described herein are capable of beingintegrated into the molecular structure of the cured polymer resultingfrom the copolymerizable of the oligomer and the alkoxylated polyolmonomer components. Integration of the surface active agent into themolecular structure of the cured polymer can be accomplished by, e.g.,covalent bonding. For example, the surface active agent can include oneor more active sites capable of establishing covalent bonds, such as,for example, unsaturated sites or reactive groups. Alternatively, thesurface active agent can be integrated into the molecular structure ofthe cured polymer by means of hydrogen bonds. In either case the surfaceactive agent possesses the advantage of not migrating within the curedcoating. Moreover, integration of the surface active agent preventswater sensitivity of the cured polymer coating which would be caused bythe presence of free surfactant.

One type of surface active agent found to be suitable for use in thecomposition of the present invention includes ethylene oxide/propyleneoxide block copolymers. Such copolymers are available from BASFCorporation under the designations PLURONIC™ P105, PLURONIC™ F108,PLURONIC™ F104, and PLURONIC™ L44, for example, and have the followingformula:

    HO--(CH.sub.2 CH.sub.2 O).sub.a --(CH(CH.sub.3)CH.sub.2 O).sub.b --(CH.sub.2 CH.sub.2 O).sub.c --H

wherein b is at least 15 and (CH₂ CH₂ O)_(a+c) is varied from 20%-90% byweight.

Another type of surface active agent suitable for use in the compositionof the present invention includes ethoxylated acetylenic alcohols anddiols such as those available under the designations SURFYNOL® 465 andSURFYNOL® 485(W) from Air Products Co. A preferred surface active agentincludes an acetylenic glycol decene diol.

Yet another type of surface active agent suitable for use in the presentinvention includes fluoropolymers and prepolymers such as, for example,fluorinated alkyl esters such as 2-N(alkyl perfluorooctane sulfonamido)ethyl acrylate which is available under designation FLUORAD FC-430 from3M Co.

Yet another type of surface active agent suitable for use in the presentinvention includes epoxy silicones such as SILQUEST A-187 available fromOSi Specialties, Inc., of Danbury, Conn., which has the formula:##STR1##

Generally, the surface active agent preferably constitutes from 0.1% to20% of the total composition, more preferably 0.5% to 10%, and mostpreferably from 1% to 5%.

Polymerization of the energy-polymerizable composition of the presentinvention may be effected by the use of, for example, electron beam (EB)radiation or ultraviolet (UV) radiation. Photoinitiators are not arequired component of the composition if EB radiation is used to effectpolymerization. However, if UV radiation is employed the compositionshould include a photoinitiator.

Any photoinitiator suitable for the purposes described herein may beemployed. Examples of useful photoinitiators include one or morecompounds selected from benzildimethyl ketal,2,2-diethoxy-1,2-diphenylethanone, 1-hydroxy-cyclohexyl-phenyl ketone,α,α-dimethoxy-α-hydroxy acetophenone,1-(4-isopropylphenyl)-2-hydroxy-2-methyl-propan-1-one,1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-propan-1-one,2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one,2-benzyl-2-N,N-dimethylamino-1-(4-morpholinophenyl)-butan-1-one,3,6-bis(2-methyl-2-morpholino-propanonyl)-9-butyl-carbazole,4,4'-bis(dimethylamino)benzophenone, 2-chlorothioxanthone,4-chlorothioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone,2,4-dimethylthioxanthone, 2,4-diethylthioxanthone,4-benzoyl-N,N-dimethyl-N-[2-(1-oxo-2-propenyl)oxy]ethylbenzenemethanaminiumchloride, methyldiethanolamine, triethanolamine, ethyl4-(dimethylamino)benzoate, 2-n-butoxyethyl 4-(dimethylamino)benzoate andcombinations thereof.

Benzophenone, which is not per se a photoinitiator, may be used inphotoinitiator compositions in conjunction with a coinitiator such asthioxanthone, 2-isopropyl thioxanthone, 4-isopropylthioxanthone,2-chlorothioxanthone, 4-chlorothioxanthone, and amine coinitiators suchas methyldiethanolamine and ethyl 4-(dimethylamino) benzoate.

It is preferable to have a blend of photoinitiators such that thecombined absorption spectra of the individual photoinitiators matchesthe spectral output of the UV lamp (or other radiation emitter) used toeffect the curing of the coating or ink composition. For example,mercury vapor lamps have strong emissions in the UV 2400 Å to 2800 Årange and in the UV 3400 Å to 3800 Å range. By choosing a suitable blendof photoinitiators a more efficient utilization of the spectral outputof the lamp can be achieved. Such increased efficiency can translate tofaster throughput during the energy-polymerization process.

Moreover, coatings employing the composition described herein caninclude colorants such as pigments and dyes which absorb UV light. Forexample, pigments generally absorb wavelengths of light below 3700 Å. Tocure such a coating one needs to generate free radicals by using aphotoinitiator which absorbs light above 3700 Å. A suitablephotoinitiator for pigmented systems includes2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one, which iscommercially available under the designation Irgacure 369 fromCiba-Geigy.

To insure that the composition does not prematurely polymerize, a freeradical inhibitor may optionally be added to the polymerizablecomposition. Examples of suitable inhibitors include hydroquinone andmethyl ether thereof or butylated hydroxytoluene at a level of from 5ppm to 2000 ppm by weight of the polymerizable components. Additiveswhich are particularly useful in prolonging the shelf-life of thecomposition can also be used, e.g. UV stabilizers such as FluorstabU.V.-II from Kromachem.

The UV radiation is preferably applied to a film of the presentcomposition at an energy density of from 2,000 to 3,000 mJ/cm², morepreferably 2,200 to 2,500 mJ/cm², in order to optimize through-curing ofthe film. While the film can be tack free with exposure to 20-40 mJ/cm²,energy densities less than 2000 mJ/cm² produce a film with a lowerdegree of crosslinking (as measured by pendulum hardness testing), andenergy densities greater than 3000 exhibit a deleterious effect on thecured film.

The composition described herein may be applied to a screen as a coatingin a conventional manner. For example, the composition can be applied bybrushes, rollers, spraying or by dipping the screen in the composition.The screen can be a mesh fabricated from, for example, silk, polyester,polypropylene, high density polyethylene, nylon, glass, and metal suchas nickel, aluminum, steel, etc. The coating composition is then curedor hardened by exposure to polymerizing radiation such as UV or EBradiation to form a blank stencil.

Generally, a six second exposure time is sufficient to cure thecomposition into a hard, tack-free coating with an energy requirement of460 kJ per kg of screen fabric.

After the screen coating is hardened, the blank stencil can be engraved,for example by means of laser light, to create porous areas in the shapeof desired indicia. The engraved screen can then be used as a mask in ascreen printing process in a conventional manner. The uncuredcomposition remaining on the application equipment is readily washablewith water.

The wettability of the composition described herein on a substrate suchas nickel can be measured by contact angle goniometry. The presentcomposition exhibits a contact angle on nickel of no more than 100°,more preferably no more than 70°, and most preferably no more than 30°.

The following examples are given for the purpose of illustrating thepresent invention.

EXAMPLE 1

A composition was made by mixing the following components:

Oligomer component:

40% of a composition containing an epoxy oligomer obtained by reacting adiglycidyl ether of bisphenol A with acrylic acid in the presence ofVersamid 335 polyamide (10%) and propoxylated glycerol triacrylate(15%).

9% dipolyoxypropylene glycerol adipate oligomer.

Monomer component:

17% trimethylol propane ethoxylate triacrylate (available from HenkelCorp. under the designation Photomer 4149).

12.5% neopentyl glycol propoxylate diacrylate (available from HenkelCorp. under the designation Photomer 4127).

6% bisphenol A ethoxylate diacrylate (available from Henkel Corp. underthe designation Photomer 4028).

Photoinitiator component:

0.5% blend of 2-isopropyl thioxanthone and 4-isopropylthioxanthone(available from International Bio-Synthetics under the designationQuantacure ITX).

2.5% 2-methyl-1-[4-(methylthio) phenyl]-2-morpholino-propan-1-one(available from Ciba-Geigy under the designation Irgacure 907).

Pigment component:

0.25% Irgalite Yellow.

Surface active agent component:

12% of ethylene oxide/propylene oxide block copolymer (available fromBASF under the designation Pluronic F-105.

The above components were mixed in accordance with the followingprocedure:

First, the epoxy acrylate oligomer, 50% of Photomer 4028, all ofPhotomer 4127, and the pigment were mixed together with grinding to forma ground paste. Next, the rest of the oligomer components were added tothe ground paste. The surfactant mixture was prepared by blending thesurface active agent with 50% of the Photomer 4149 under mild heating(less than 35° C.). The surfactant blend was then added at roomtemperature to the ground paste with stirring. The photoinitiator wasmixed with the remaining 50% of the Photomer 4149 and then added to theground paste with mixing.

The resulting composition was self-emulsifying, had a viscosity of 2300centipoise, and exhibited thixotropic shear thinning characteristics.

The composition was applied as a 2 mil thick film to screen substratesof aluminum, nickel, and steel mesh and then cured by passing thesubstrates under a U.V. lamp under the following conditions:

    ______________________________________                                        Lamp:                 Hg vapor                                                  Power: 300 watts/cm                                                           Conveyor speed: 20 ft./min.                                                   Exposure time: 6 seconds                                                      Exposure temperature: 25° C.                                         ______________________________________                                    

The film was observed to be tack free after one pass. The followingtests were performed on the cured film.

Wettability of the metal substrates by the composition was measuredusing a contact angle goniometer at room temperature. The contact angleof the UV cured epoxy acrylate based film of this Example was found tobe 27.5 degrees.

The hardness of the cured film, one indicator of crosslink density, wasmeasured in accordance with ASTM D4366-92 Pendulum damping test. Thecured film exhibited a hardness of 157 counts as measured by this test.

The solvent resistance of the cured film was measured by the ASTMD5402-93 MEK double rub test. The cured film was measured at more than200 double rubs.

Adhesion of the film was assessed by a conventional tape test and byscanning electron microscope. The film exhibited sufficient adhesion.

EXAMPLE 2

A composition was made by mixing the following components:

Olizomer component:

37.3% of a composition containing epoxy oligomer obtained by reacting adiglycidyl ether of bisphenol A with acrylic acid in the presence ofVersamid 335 polyamide (10%)and propoxylated glyceryl triacrylate (15%).

Monomer component:

18.66% trimethylol propane ethoxylate triacrylate (Photomer 4149).

9.33% neopentyl glycol propoxylate diacrylate (Photomer 4127).

13.99% bisphenol-A-ethoxylate diacrylate (Photomer 4028).

Photoinitiator component:

9.52% blend of Quantacure 369 (available from International BioSynthetics and Darocur 4265 (available from Merck).

Pigment component:

1.87% Irgalite yellow.

Surface active agent component:

9.33% Ethylene oxide/propylene oxide copolymer (Pluronic 105 availablefrom BASF).

The composition of this Example was prepared in accordance with themixing method of Example 1. The composition was water washable. It had aviscosity of 3500 centipoise and exhibited thixotropic shear thinningcharacteristics.

The composition was applied to a nickel screen substrate and then curedby passing the substrate under a UV lamp under the same conditions asset forth in Example 1.

The sample was observed to be tack free after one pass. The contactangle measured by a goniometer as an indicator of wettability was 27.5.

EXAMPLE 3

A composition was made by mixing the following components:

Oligomer component:

40% of a composition containing epoxy oligomer obtained by reacting adiglycidyl ether of bisphenol A with acrylic acid in the presence ofVersamid 335 polyamide (10%) and propoxylated glyceryl triacrylate(15%).

9% dipolyoxypropylene glycerol adipate oligomer.

Monomer component:

17% trimethylol propane ethoxylate triacrylate (Photomer 4149).

13% neopentyl glycol propoxylate diacrylate (Photomer 4127.

6% bisphenol-A-ethoxylate diacrylate (Photomer 4028).

Photoinitiator component:

3% 2-benzyl-2-N,N-dimethylamino-1-(4-morpholinophenyl)-1-butanoneavailable as Irgacure 369.

1% thioxanthone

Pigment component:

1% Phthalo Blue GS

Surface active agent component:

10% Ethylene oxide/propylene oxide copolymer (Pluronic 108 availablefrom BASF).

The composition of this Example was prepared in accordance with themixing method of Example 1. The composition was water washable andexhibited thixotropic shear thinning characteristics.

EXAMPLE 4

A composition was made by mixing the following components:

Oligomer component:

25% of a composition containing epoxy oligomer obtained by reacting adiglycidyl ether of bisphenol A with acrylic acid in the presence ofVersamid 335 polyamide (10%) and propoxylated glyceryl triacrylate(15%).

Monomer component:

27.25% trimethylol propane ethoxylate triacrylate (Photomer 4149).

8% neopentyl glycol propoxylate diacrylate (Photomer 4127).

30% bisphenol-A-ethoxylate diacrylate (Photomer 4028).

Photoinitiator component:

2.5% Irgacure 369

0.94% thioxanthone

Pigment component:

0.31% Phthalo Blue GS

Surface active agent component:

6% Ethylene oxide/propylene oxide copolymer (Pluronic 108 available fromBASF).

The composition of this Example was prepared in accordance with themixing method of Example 1. The composition was water washable andexhibited thixotropic shear thinning characteristics.

While the above description contains many specifics, these specificsshould not be construed as limitations on the scope of the invention,but merely as exemplifications of preferred embodiments thereof. Thoseskilled in the art will envision many other possible variations that arewithin the scope and spirit of the invention as defined by the claimsappended hereto.

What is claimed is:
 1. A substantially water-free, water-washable,energy-curable, polymer-forming composition which comprises:a) anoligomer selected from the group consisting of epoxy oligomer andurethane oligomer, said oligomer having at least two ethylenicallyunsaturated moieties; b) at least one alkoxylated polyol monomer havingat least two ethylenically unsaturated moieties and capable of beingcopolymerized with oligomer component (a) to provide a solid curedpolymer when exposed to energy-polymerizing conditions; and, c) at leastone surface active agent capable of being integrated into the molecularstructure of the polymer resulting from the copolymerization of (a) and(b) either by covalent bonding or by hydrogen bonding, and furthercapable of rendering said composition water-dispersible.
 2. Thecomposition of claim 1 wherein the epoxy oligomer is obtained byreacting a diepoxide with an acid component having an ethylenicallyunsaturated carboxylic acid or reactive derivative thereof in thepresence of a polyamide derived from a polymerized fatty acid.
 3. Thecomposition of claim 2 wherein the acid component is acrylic acid. 4.The composition of claim 3 wherein the diepoxide is a diglycidyl etherof a dihydric phenol.
 5. The composition of claim 1 wherein thealkoxylated polyol monomer has the formula:

    R.sup.2 --[--(Y).sub.x --R.sup.3 --CH═CH--R.sup.4 ].sub.n

wherein R¹ is an aliphatic, aromatic, or arene moiety having at leasttwo carbon atoms and at least two oxido residues, Y is an alkylene oxidemoiety and x is an integer of from 2 to about 6, R³ is a linkage groupcapable of joining the alkylene oxide moiety Y and the --CH═CH-- group,R⁴ is hydrogen or --C(O)OR⁵ wherein R⁵ is hydrogen or an alkyl grouphaving from 1 to about 22 carbon atoms, and n is an integer of from 2 toabout
 6. 6. The composition of claim 5 wherein R² is a bisphenolresidue.
 7. The composition of claim 5 wherein R² is selected from thegroup consisting of ethylene glycol residue, propylene glycol residue,trimethylolpropane residue, pentaerythritol residue, neopentyl glycolresidue, glyceryl residue, diglyceryl residue, inositol residue, andsorbitol residue.
 8. The composition of claim 5 wherein Y is an ethyleneoxide residue.
 9. The composition of claim 5 wherein the at least onealkoxylated polyol monomer comprises a mixture of at least onealkoxylated polyol diacrylate and at least one alkoxylated polyoltriacrylate.
 10. The composition of claim 9 wherein said compositionexhibits a contact angle on nickel of no more than about 100°.
 11. Thecomposition of claim 9 wherein said composition exhibits a contact angleon nickel of no more than about 70°.
 12. The composition of claim 9wherein said composition exhibits a contact angle on nickel of no morethan about 30°.
 13. The composition of claim 9 wherein the compositionincludes from about 5% to about 30% of the at least one alkoxylatedpolyol diacrylate and from about 5% to about 30% of the at least onealkoxylated polyol triacrylate based on total composition weight. 14.The composition of claim 9 wherein the composition includes from about15% to about 20% of the at least one alkoxylated polyol diacrylate andfrom about 15% to 20% of the at least one alkoxylated triacrylate basedon total composition weight.
 15. The composition of claim 1 wherein Thesurface active agent possesses at least one unsaturated site, thesurface active agent being integrated into the molecular structure ofthe polymer by covalent bonding upon curing of the composition.
 16. Thecomposition of claim 15 wherein the surface active agent includes acompound having at least one acetylenic bond.
 17. The composition ofclaim 1 wherein the surface active agent includes an acetylenic glycoldecene diol.
 18. The composition of claim 1 further including aphotoinitiator.
 19. The composition of claim 18 wherein thephotoinitiator is at least one member selected from the group consistingof benzildimethyl ketal, 2,2-diethoxy-1,2-diphenylethanone,1-hydroxy-cyclohexyl-phenyl ketone, α,α-dimethoxy-α-hydroxyacetophenone, 1-(4-isopropylphenyl)-2-hydroxy-2-methyl-propan-1-one,1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-propan-1-one,2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one,2-benzyl-2-N,N-dimethylamino-1-(4-morpholinophenyl)-butan-1-one,3,6-bis(2-methyl-2-morpholino-propanonyl)-9-butyl-carbazole,4,4'-bis(dimethylamino)benzophenone, 2-chlorothioxanthone,4-chlorothioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone,2,4-dimethylthioxanthone, 2,4-diethylthioxanthone,4-benzoyl-N,N-dimethyl-N-[2-(1-oxo-2-propenyl)oxy]ethylbenzenemethanaminiumchloride, methyldiethanolamine, triethanolamine, ethyl4-(dimethylamino)benzoate, 2-n-butoxyethyl 4-(dimethylamino)benzoate andcombinations thereof.
 20. The composition of claim 1 further including acolorant.
 21. The composition of claim 20 wherein the colorant is a bluepigment and the composition further includes a2-benzyl-2-N,N-dimethylamino-1-(4-morpholinophenyl)1-butanone andthioxanthone.
 22. A substantially water-free, water-washable,energy-curable, polymer-forming composition which comprises:a) anoligomer selected from the group consisting of epoxy oligomer andurethane oligomer, said oligomer having at least two ethylenicallyunsaturated moieties; b) at least one alkoxylated polyol monomer havingat least two ethylenically unsaturated moieties and capable of beingcopolymerized with oligomer component (a) to provide a solid curedpolymer when exposed to energy-polymerizing conditions; and, c) at leastone surface active agent capable of being integrated into the molecularstructure of the polymer resulting from the copolymerization of (a) and(b) either by covalent bonding or by hydrogen bonding, and furthercapable of rendering said composition water-dispersible, wherein the atleast one alkoxylated polyol monomer comprises a mixture of at least onealkoxylated polyol diacrylate and at least one alkoxylated polyoltriacrylate, and wherein the at least one alkoxylated polyol triacrylateis trimethylolpropane ethoxylate triacrylate and the at least onealkoxylated polyol diacrylate is a member selected from the groupconsisting of bisphenol A ethoxylate diacrylate, neopentyl glycolpropoxylate diacrylate and mixtures thereof.
 23. The composition ofclaim 22 wherein the epoxy oligomer is derived from bisphenol A epoxydiacrylate.
 24. The composition of claim 22 wherein the monomer mixtureincludes from about 10% to about 15% by weight of neopentyl glycolpropoxylate diacrylate, and from about 15% to about 20% by weight oftrimethylolpropane ethoxylate triacrylate, based on total compositionweight.
 25. The composition of claim 24 wherein the monomer mixturefurther includes from about 5% to about 10% bisphenol A ethoxylatediacrylate.
 26. The composition of claim 24 wherein the epoxy oligomeris obtained by reacting a diepoxide with an acid component having anethylenically unsaturated carboxylic acid or reactive derivative thereofin the presence of a polyamide derived from a polymerized fatty acid.27. The composition of claim 26 wherein the acid component is acrylicacid.
 28. The composition of claim 27 wherein the diepoxide is adiglycidyl ether of a dihydric phenol.
 29. A screen coated with acoating material comprising:a) an oligomer selected from the groupconsisting of epoxy oligomer and urethane oligomer, said oligomer havingat least two ethylenically unsaturated moieties; b) at least onealkoxylated polyol monomer having at least two ethylenically unsaturatedmoieties and capable of being copolymerized with oligomer component (a)to provide a solid cured polymer when exposed to energy-polymerizingconditions; and, c) at least one surface active agent capable of beingintegrated into the molecular structure of the polymer resulting fromthe copolymerization of (a) and (b) either by covalent bonding or byhydrogen bonding, and further capable of rendering said compositionwater-dispersible.
 30. The screen of claim 29 wherein said screen isfabricated from a material selected from the group consisting of silk,polyester, polypropylene, high density polyethylene, nylon, glass,nickel, aluminum and steel.
 31. The screen of claim 29 wherein thecoating material further comprises a photoinitiator.
 32. The screen ofclaim 29 wherein the epoxy oligomer is obtained by reacting a diepoxidewith an acid component having an ethylenically unsaturated carboxylicacid or reactive derivative thereof in the presence of a polyamidederived from a polymerized fatty acid.
 33. The screen of claim 29wherein the alkoxylated polyol monomer has the formula:

    R.sup.2 --[--(Y).sub.x --R.sup.3 --CH═CH--R.sup.4 ].sub.m

wherein R² is an aliphatic, aromatic or arene moiety having at least twocarbon atoms and at least two oxido residues, Y is an alkylene oxidemoiety and x is an integer of from 2 to 6, R³ is a linkage group capableof joining the alkylene oxide moiety Y and the --CH═CH-- group, R⁴ ishydrogen or --C(O)OR⁵ wherein R⁵ is hydrogen or an alkyl group of from 1to 22 carbon atoms, and m is an integer of from 2 to
 6. 34. The screenof claim 33 wherein R² is selected from the group consisting ofbisphenol residue, ethylene glycol residue, propylene glycol residue,trimethylolpropane residue, pentaerythritol residue, neopentyl glycolresidue, glyceryl residue, diglyceryl residue, inositol residue, andsorbitol residue.
 35. The screen of claim 29 wherein said coatingmaterial is cured.
 36. The screen of claim 35 wherein the screen isengraved with indicia.